.content {
    width: 640px;
    height: 640px;
    margin: 100px auto;
    position: relative;
}
.btn {
    width: 100%;
    height: 100%;
    position: absolute;
    left: 0;
    top: 0;
    background-color: rgba(0,0,0,.5);
    z-index: 2;
}
.btn button {
    width: 100px;
    height: 50px;
    cursor: pointer;
    background-color: #225675;
    border: none;
    position: absolute;
    left: 50%;
    top: 50%;
    border-radius: 30px;
    transform: translate(-50%,-50%);
    color: aliceblue;
    font-size: 16px;
}
.pauseBtn {
    display: none;
}
#snakeWrap {
    width: 600px;
    height: 600px;
    position: relative;
    background-color: #225675;
    border: 20px solid #7dd9ff;
}
/* 贪食蛇本体 */
.snakeHead {
    width: 20px;
    height: 20px;
    border-radius: 50%;
    background-color: red;
}
.snakeBody {
    width: 20px;
    height: 20px;
    border-radius: 50%;
    background-color: green;
}
/* 蛇的目标 */
.food {
    width: 20px;
    height: 20px;
    border-radius: 50%;
    background-color: pink;
}